The present invention relates to a high-speed electric system and in particular to a system comprising a single-phase permanent-magnet electric machine.
Single-phase, permanent-magnet electric machines are driven by commutating current in a single phase winding. As the speed of the electric machine increases, the back emf in the phase winding increases. It therefore becomes increasingly difficult to drive current and thus power into the phase winding. Additionally, in a single-phase machine rotor losses are generally high due to armature reaction disturbing the field in the magnet. Accordingly, high-speed systems generally comprise an electric machine having three or more phases. However, this provision of additional phases increases the cost of the electric system.